Compressor system



ug. 31, 1948. B. w. MANTLE 2,448,379

COMPRESSOR SYSTEM Filed July 19, 1946 3 Sheets-Sheet l Aug. 3l, 1948. B. w. MANTLE COMPRESSOR SYSTEM I5 Sheets-Sheet 2 Filed `July 19, 1946 NWN Aug. 31, 1948. B. w. MANTLE COMPRESSOR SYSTEM 3 Sheets-Sheet 3 Filed July 19, 1946 j N NNN Patented Aug. 3l, i948 DFFICE COMPRESSOR SYSTEM Burr W. Mantle, Pittsf American Brake Shoe Company, N. Y., a corporation of Delaware ord, N. Y., assignor to New York,

Application July 19, 1946, Serial No. 684,654

13 Claims.

The present invention relates to a compressor system and particularly to a dual capacity air compressor system of the general character described in my prior Patent No. 2,253,859, patented August 26, 1941. The present invention has to do more particularly with a number of improvements over the system described in the aforesaid patent with a view to changing from one type of operation to another by a simple control movement which changes automatically the necessary safety valve settings, pulley arrangements and the like.

In garages, shops, service stations and the like, it is desirable to have an air compressor system capable of supplying compressed air at a relatively high pressure, for example 125 to 150 pounds per square inch, for inlating pneumatic tires, operating equipment employing pneumatic motors, and the like. It is also desirable to have a low pressure system where a relatively large supply of air may be made available at a pressure range, for example, of 40 to 50 pounds per square inch, for operating paint spray guns and the like. In large shops it may be economical to provide separate systems but in smaller shops and stations it is desirable to have a single system capable of both types of operation.

The system described in my aforesaid patent I provides for the operation of a compressor at two different rates of speed for high pressure low volume output and low pressure high volume output respectively. However, the system therein described requires manual changes in pulley adjustments and the like. It depends, furthermore, among other things, upon a thermal overload device for protecting an electric driving motor against injury, in case the compressor should be s et to operate. for example, at high pressure and at high speed. for high volumetric output at the same time. This arrangement is objectionable, even though the motor is amply protected against burning out, since it interferes with continuous operation of the system.

It is, therefore, an obiect of my invention to place various safety devices and speed adjusting means for a dual capacity compressor system under the direct and positive control of a single master control element.

An additional object is to prevent overloading of a drive motor by positively operated means so arranged that movement of a control device to change the operating speed of a compressor driven by such motor is effective to produce a correlative change in the maximum output pressure of such compressor.

Still another object of my invention is to interrelate the various controls and safety devices of a dual capacity compressor system so that they can be operated directly by manipulation of a single manual control element, thus eliminating the possibility of having certain controls and devices set for one type of operation, while others are set for another type of operation.

A further object of my invention is to mount a compressor and a drive motor therefor in such `a manner that they can be moved relatively, the

drive arrangement between them being such that said relative movement is effective automatically to change their speed ratio, and the arrangement being such that unloader mechanism for the compressor is automatically and selectively rendered operative or inoperative by said relative movement.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show a preferred embodiment of the present invention and the principles thereof and what I now consider to be the best mode in which I have contemplated applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

Fig. 1 is a perspective view of a compressor unit or system embodying my invention;

Fig. 2 is a plan view of the unit shown in Fig. 1 on a somewhat larger scale, part of the pressure tank being broken away;

Fig. 3 is a fragmentary elevational view taken substantially along the line 3 3, Fig. 2, this view being on a somewhat larger scale than Fig. 2, with certain parts broken away and parts shown in section;

Fig. 4 is a transverse sectional view taken substantially along the line fin-5, Fig. 2;

Fig. 5 is an enlarged sectional detal view of a relief valve whch comprises a part of my invention, this view being taken substantially along the line '5-5, Fig. 2; and

Fig. 6 is an enlarged sectional detail view taken substantially along the line 6 6, Fig. 2.

Referring rst to Fig.- l of the drawings, there is shown an air compressor system comprising a storage tank ii which supports a compressor, a drive motor. and certain control mechanisms to be described hereinafter.

The storage tank ii is of suitable size, shape and thickness for storing compressed air, or other compressed fluid, at a pressure up to the maximum pressure required for the service intended. rlihe tank is mounted on suitable supports or feet i2, it which hold it in upright position.

A platform ifi is mounted on top of the tank ii for supporting a compressor and motor and downturned side flange portions I5, I5A, I6 and IBA, which provide feet to rest on the cylindrical surface of the tank II. These feet or flanges are secured firmly to the tank, preferably by welding, so that the platform is rigidly mounted, providing a firm base for the motor and compressor.

An air compressor I1 is mounted on one end of the platform by suitable means such as studs or bolts I8. This compressor may be of any appropriate type, but as shown it comprises a crank case I9, a cylinder 28 provided with cooling fins 2|, a shaft 22 for driving the compressor (Fig. 2) and a pulley 23 for driving shaft 22. The pulley has a grooved rim, as shown at 24, for a V'-belt or the like 25, and it may comprise spokes 26 which are beveled or twisted propellers for causing a rapid circulation of air over the compressor to facilitate its cooling.

An air intake 21, which may comprise a filter, if desired, is mounted on top of the compressor and an outlet or exhaust tube 28 leads from the cylinder to form a cooling loop and connects to the pressure tank by means of a tubing nut 29 and a check valve 38 that is threaded into a suitable opening in the tank I I. The tube 28 may be provided with cooling fns 3| to radiate heat to the atmosphere, the tube thus serving as an after cooler to reduce the temperature of the compressed air before it reaches the storage tank.

At the end of the tank II opposite that to which connection 28 is attached, an outlet connection 32 is provided. This connection leads to a six-way connector to which are attached a valve 33 for the pneumatic line, a high pressure safety valve 34', a low pressure gauge 36 and a switch 31.

Air pressure applied through the connection 32 operates the pressure gauge 36 which may be of any standard type. The low pressure relief valve 35 is operated under some conditions and is rendered inoperative vunder others, as will be more fully described hereinafter. The high pressure safety valve 34 is effective to release air from the tank when a maximum allowable pressure has been reached. The pressure controlled electric switch 31, which may be of conventional type and is well known, per se, in the prior art, functions to energize or deenergize an electric power circuit to a drive motor 38 of suitable character. An electric cable 39 connects the switch 31 with motor 38. The valve 33, of course, is manually controlled, being normally left open so that air is supplied through a suitable pipe or hose to the devices which operate thereby.

The motor 38 may be an electric motor of appropriate size and type or, if desired, it may be a gasoline motor. It is mounted adjustably on a plate or base 48 which, in turn is slidably mounted on the platform I4 in a manner and by means which will be described presently. Motor 38 comprises a drive shaft 58 which operates an adjustable pulley 5l suitably secured to shaft 58 for rotation therewith.

The pulley 5I is of the type that enables the pitch diameter type thereof to be adjusted automatically as an incident to changes in the spacing of the axes of the driving and driven pulleys, and such adjustable pulleys are known per se in the prior art. It is comprised of two halves, disclike members 52 and 53 which oppose each other to provide a V-groove for a V-belt or the like, and

pressure controlled electric like fan blades or relief valve 35, a pressure tions slidably mounted in slots 66.

4 the effective pitch is determined by the spacing between the halves 52 and 53. Both of the inner discs 52 and 53 are xed on the motor shaft in a rotative sense, and are arranged for relative axial movement in which either one or both of the discs may move relative to the motor shaft. As herein shown, the disc 52 is fixed to the shaft 58,

The V-belt or the like 25, mentioned above, passes about the pulley 5I,or between the two halves 52 and 53 thereof, and its position between such halves obviously determines the effective pitch diameter of pulley 5|. If the motor 38 and compressor I 1 are moved farther apart, increased tension causes the belt 25 to wedge the pulley halves 52, 53 away from each other and the belt moves to a smaller effective pitch diameter. As a result the compressor is driven more slowly. On the other hand, if the motor is moved closer to the compressor, tension ,is reduced and the belt 25 climbs outwardly on pulley 5I and the spring means mentioned above moves the outer half 53 toward the opposing member 52 to increase the effective pitch diameter. As a result, the compressor is driven more rapidly, assuming that the motor shaft 58 continues to operate at the same speed.

The movable plate 48 which supports the motor 38 comprises a substantially flat member of suitable material, such as cast or forged metal, provided with downturned edge flanges 6I, 62, 83 and 64' and reinforcing ribs 65. as best shown in Fig. 2. The platform |4 is provided with longitudinal openings or s'lots 66 in which bolts 61 are slidably mounted. These bolts pass through openings 68 in boss portions 89 provided on the lower surface of member 48 and they pass through spacers 18 which have head portions 1I wider than the slots and have their reduced sleeve por- A nut 12 and washer 13 on each of the bolts 61 seat in a recess 14 provided in the upper surface of the member 48 foreach of the openings 68. The spacers 18 permit tightening of the nuts 12 without preventing free sliding movement of the plate or base member 48 along the platform member I4. See Fig. 3.

The motor 38 is supported on a bracket 8| secured thereto as by bolts 82 and welded or otherwise fastened to a plate 83, Fig. 3. The plate 83 is provided with longitudinal slots 84 through which bolts 85 may be secured. These bolts have their heads seated in recesses 86 provided in boss elements 81 on the lower surface of the base member 4'8 and are passed through openings 88 therein as best shown in Fig. 6. By means of a nut 89 and washer 9| each of the bolts 85 may be tightened to hold the plate 83 in adjustment with respect to the base member 48. Hence the motor is adjustable with respect to the base 48 and the base 48 is slidably mounted with respect to the platform I4 and the compressor I1 supported thereby.

A lever I8I is provided for shifting the base member 48 longitudinally so as to move the motor 38 toward or away from the compressor and thus cause the pulley 5I, through tension applied to the belt 25, to change its effective diameter in the manner described above. This lever bears a downwardly projecting stud |82 at its rear end, or at the left as seen in Fig. 4, which engages in an opening |83 provided in the platform member it. Forwardly of the stud |02 the lever bears another stud |04 which projects upwardly into an opening |05 formed in a boss portion |06 on the lower side of the base member 40. The stud im serves as a fulcrum and the stud |04 causes the slidable motor-supporting base member 40 to move as the lever |ll| is moved between the full line position at the right and the dotted line position at the left as shown in Fig. 2.

The lever ||i| is arranged to spring upwardly at its forward end and is provided with a grip |01 of suitable material such as hard rubber, plastic, or the like. Thefront ange 62 of the base member 4|| is notched at two points, as shown at iii and H2, Fig. 3, to latch or retain the lever mi in either of the two positions shown in Fig. 2. When the lever is moved to the right, Fig. 2, to its full line position, the motor is advanced toward the compressor and tension on belt 25 is reduced, permitting the pulley 5| to close and thereby increase the effective pitch of the pulley 5|. This increases the speed at which the compressor is driven, assuming that the motor operates at a substantially constant speed. Indicia 50," cast or otherwise formed on the base t adjacent the notch indicate the general pressure range at which the compressor may be operated when thus set without overloading the motor.

When the lever mi is shifted to the dotted line position, Fig. 2, the base 4|) is moved to the left as seen in said figure, increasing the distance between the motor 33 and the compressor i1 so as to apply increased tension to the belt 25. This tension causes the belt 2t to wedge the two halves t2 and 53 of the drive pulley 5| away from each other so that the belt rides inwardly of the periphery of the drive pulley, thereby reducing its effective pitch diameter. The result of this is that the motor drives the compressor at a slower rate of speed, again assuming that the motor operates at a substantially constant speed. Hence the compressor may be operated at greater output pressure although its volumetric output is reduced. The indicia 150 cast or otherwise formed on the base i3 adjacent the notch ||2 indicate the general pressure range at which the compressor may be operated when the lever is shifted to this position.

Mention was made hereinabove of the low pressure relief valve 35 and the high pressure safety valve 3d. When the compressor is being driven at high speed, that is when the lever ii is in its full line position, Figs. 1 and 2, it is necessary that the tank pressure be limited so that the motor will not be over-loaded. The valve 35 is designed to release air from the tank i whenever pressure exceeds that required for the lower pressure type of operation. This pressure range may be of the order of 50 pounds per square inch as previously mentioned, although different pressure may be selected when the apparatus is designed for other uses or types of use.

The low pressure relief valve 3b comprises a body member |2| provided with a threaded connection |22 preferably of the tapered type which fits into the six way connection mentioned above and indicated at |23, Fig. 2. A portion of this connection is shown also in Fig. 5.

The body member iti connects with the member |23 through a port |22 which is closed by a valve member |25.- As shown in Fig. 5' the valve member |25 may be substantially spherical in form and adapted to rest in a valve seat |26 under the pressure of a spring |21 which surrounds .a

' pounds per square valve stem |28 secured to the spherical member |25.

The member |2| is threaded internally at its outer end and an adjustable bushing |3| is threaded as indicated at |32 to fit into the threaded connection just mentioned. A lock nut |33 is provided for holding the member |3| in any position of adjustment. An opening |35 leads to the atmosphere from the chamber |33 in which the valve closing member |25 is mounted.

By means of the construction :lust described,

air in the tank is released to the atmosphere,

whenever its pressure exceeds the lower operating pressure of the compressor, as indicated when the lever |0| Iis in its full line position shown in Figs. l and 2. In case air is not being drawn from the supply valve 33, the compressor i1 may continue to operate, the valve member |25 being lifted off its seat |26 to permit continuous release of air through the ports |24 and |35.

When it is desired to operate the compressor at its high pressure range, means are provided for holding the low pressure relief valve 35 inoperative. As shown in Fig. 3, a bar |4| is slidably mounted between the platform I4 and the base member 40, an upturned end |42 of this bar being received Within a recess |43 formed in the lower surface of the base member 40. A compression spring |44 is also mounted in the recess |43 in such a manner as to urge the bar |4| to the left as seen in Figs. 2 and 3. The outer end of the bar |4| is bent downwardly so as to cooperate with the head |46 of the valve stem |28 mentioned above.

As long as the unit is adjusted for low pressure operation, the bar |4| has no effect on the valve 35 and the latter is free to operate and prevent over-loading of the compressor. However, when the lever is shifted to the left as seen in Figs. 1 and 2 to the dotted line position shown, the downturned end |45 of the bar |4| tends to push the valve stem |28 inwardly. The spring |44 is placed under compression and thus applies its effeet to augment the eiect of spring |21 to hold the valve |25 tightly on the valve seat |26. The combined effect of the two springs |21 and |44 is such that the valve |25 remains closed at pressures equal to, or above the higher maximum pressure of the high pressure range, as determined by the high pressure safety valve 34.

Hence when the compressor unit is operating in the high pressure range the relief valve 35 remains closed for normal operation and the safety valve 34 becomes operative. The valve 34 is similar to or identical with valve 35 in internal construction except that a stronger spring tension is employed and the valve is otherwise designed to open only when a maximum allowable pressure is exceeded. In the example given above, this pressure might be of the order of inch, although it may be varied as desired within the limits set by the design of the equipment.

From the above description it will be apparent that by simply moving the lever |0| to either of the positions shown in Fig. 2, all the necessary controls may be set for operating the compressor unit at the desired range. When the unit is set for low pressure operations the low pressure relief valve becomes operative to limit the working pressure and the belt 25 automatically climbs to the outer position on the drive pulley 5| so as to operate the compressor at a relatively high rate of speed with good volumetric output. When the compressor unit is set for operation in the high pressure range, the relief valve 35 is rendered inoperative as described above, thereby placing the safety valve 34 in operation to limit maximum pressure, and at the same time the pulley adjusts itself to a smaller effective pitch diameter to drive the compressor at a slower rate. of speed and thereby avoid over-loading the motor.

Although the description given above refers to the use of an electric motor, and the cable 39 by which the pressure switch 31 controls the motor would normally be the conductor for the line current, the same general type of control might be used in the conventional way in connection with a gasoline motor, in which ease a reverse acting switch would be employed in the unit 31 to short circuit the magneto of the engine when the engine is to be cut off or stopped.

For low pressure operation the lever ||l| is set as indicated in Fig. 1, and as shown in full lines in Fig. 2, and if air is not used as rapidly as it is being compressed, the excess is vented to the atmosphere through the low pressure relief valve 35 in the manner described above, and since the pressure in the tank is thus maintained far below the cut-off value of the switch 31, the motor 38 will operate continuously.

For high pressure operations the compressor is driven at a lower rate of speed, the relief valve 35 is rendered inoperative in the manner de scribed above, and the pressure switch 31 normally controls operation of the motor. This switch, as is well known in the art, is so designed that the motor will be placed in operation when pressure in the tank drops to a minimum for the higher operating range, for example 120 pounds per square inch. This minimum may of course be adjusted to any desired figure consistent with the design of the unit. The motor then operates continuously until the pressure reaches a predetermined maximum, whereupon the switch 31 cuts off the current to the motor. This maximum may be varied, since switch 31 can be adjusted to the desired gure, for example 150 pounds per square inch. As long as the pressure switch operates properly, the safety valve 34 may remain closed, since it will normally be set to open at a slightly higher pressure than required to operate the switch 31 to cut 01T the motor. However, if for any reason the pressure switch 31 fails to cut off the motor, the safety valve 34 will open and prevent building up dangerous or excessivepressure within the system.

Although I have described the invention above in connection with an air compressor unit of a particular type, it will be understood that my invention is not necessarily limited thereto, but it may be applied to other types of compressors, and may be used in connection with the compression of uids other than air. As pointed out above, the motor may be either electric orv gasoline and the pressure ranges may be chosen as desired, within the limitations of the design of the equipment, appropriate choices being made of the self-adjusting pulley 5| the safety valves 35 and,34, the pressure switch 31, and other oper- ,ating parts.

The power required to operate a compressor is roughly proportional to the product of the operating speed or volumetric output rate multiplied by the output pressure. Temperature rises, of course, cause departures from an exact ratio. Since it is desirable to obtain maximum operating elciency of the motor and at the same time avoid objectionably overloading it, the variable pulley 5| should be so designed as -to change its effective pitch diameter and the Vspeed at which it .drives the compressor so that such efficiency is attained in both settings of the apparatus. Thus, in the example given above, where-the operating ranges are about 50 and 150 pounds per square inch for low and high pressure, respectively, the pulley may be designedto drive .the compressor approximately one and one-half times as fast at low pressure as at high pressure. It will be noted, however, that both the lower and the higher pressure ranges may be varied considerably by adjusting the low pressure relief valve 35 and/or the high pressure safety valve 3|. Hence the design of pulley 5|, or the extent to which its pitch diameter may be varied in moving the motor from one positin to the other, may be chosen to fit the intended operating ranges.

The extent to which the pulley 5| changes its eective pitch diameter depends on the changes in tension on belt 25. This is a function of the distance through which the motor is moved, and can be varied as desired to obtain the required operating speeds. The essential criterion is that the compressor should be driven, in either the low pressure or the high pressure range, at a speed that involves eflicient motor operation without objectionable overload.

While I have described the motor 38 as being movably mounted on the frame for the purpose of changing the tension on belt 25 and thereby effecting a shift from one pitch diameter to another on the driving pulley 5|, it will be understood that other means might be utilized for accomplishing the same result. For example, a shiftable idler roller applied to the belt might be used to change its tension or eifectivelength and to thereby effect a change in pitch diameter of pulley 5| without moving the motor. It will be apparent that this and other equivalents vfall within the scope of my invention and the claims are intended to cover such scope. This alternative arrangement is not shown, being considered obvious in view of the above discussion.

As described above, it is preferred to use a safety valve 34 for high pressure operation, in addition to the low pressure valve 35 which normally operates only when the motor is shifted toward the compressor, lever |0| being in theA full line position of Figs. 1 and 2. However, the spring |44 which is effective to augment the force of spring |21, may be so chosen, and the pressure applied thereto so adjusted, that when the lever |0| is shifted to the dotted line posi-l tion, Fig. 2, the valve 35 becomes a high pressure safety valve. In this case, the valve 34 may be eliminated. For exibility in setting both the upper and lower pressure ranges, however, the use of both valves is..considered preferable.

Thus, while I have illustratedrand described the preferred embodiment of. my invention, it is to be understood that this is capable of variation and modification and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims. f

I claim: 1. In a compressed air supply system, the combination which comprises an air compressor including a driven pulley, a driving motor` including a variable pitch diameter drive pulley arranged to change said pitch diameter according to tension on a belt er. se

' ing said a drive belt for connecting said pulleys, vmovable means for changing the tension on said belt to cause said drive pulley to change its pitch diameter, and valve means controlled by said movable means for regulating the output pressure of said compressor in correlation with the speed of saidcompressor.

2. In a dual capacity compressed air system, a movably mounted motor, means for moving said motor, means driven by said motor for operating a compressor at a high rate or a low rate of speed depending upon the position of said motor, and means for limiting maximum pressure to a low level when said compressor is operated at a high rate, said last named means being rendered inoperative when said motor is moved to operate said compressor at a low rate of speed.

3. In a compressed air supply system, a relief valve comprising a spring pressed closure element, movable means for changing the volumetric output rate of said system, and resilient means controlled by said movable means for element and thereby to increase the pressure range at which said relief valve becomes operative when said volumetric rate is reduced.

4. In a compressed air supply system, the combination of a` pressure relief valve operable at a low pressure range, and a safety valve operable at a high pressure range, resilient means for holding said relief valve closed below said low pressure range, and other resilient means effective to augment said first named resilient means and hold said relief valve closed at pressures below said high pressure range.

5. In a compressed air system, the combination of a compressor, a drive motor, a belt pulley on said motor for driving said compressor, said pulley being of automatically variable pitch diameter dependent upon belt tension, movable means for varying said tension to cause said pulley to assume a large pitch diameter in one position and a small pitch diameter in another position; and a relief valve for limiting maximum pressure when said pulley assumes large pitch diameter, said valve being rendered inoperative by said movable assumes a small pitch diameter.

6. In a compressed air system, the combination of compressor means operable at either va high or a low volumetric output rate, a shiftable member for controlling the volumetric rate selectively, and pressure limiting means controlled by said shiftable member for maintaining relatively high pressure when the volumetric output rate is low and for maintaining a lower pressure when the volumetric output rate is high.

'1. In a compressed air supply system, the comfbination of a compressor having a driven pulley, a motor having a drive pulley ccf variable pitch diameter, a belt connecting said pulleys, means for changing said pitch diameter to change the speed at which said compressor is driven by said motor, a pressure switch for stopping and startmotor automatically at the higher and lower limits of a high pressure operating ran-ge, and a relief valve controlled by said changing means for relieving the output pressure of said compressor below said high pressure range when said compressor rate of speed.

is driven at a comparatively high.

presser -to means when said pulley salid variable pulley,

8. In a compressed air supply system, fthe combination of a compressor having a driven belt pulley, a driving motor having a variable pitch diameter belt pulley, a belt connecting said pulleys, movable means for changing the tension on'said belt and -thereby changing the effective pitch of said variable pulley, and plural pressure relief valve means selectively controlled by said movable means.

9. In combinati-on a variable pitch drive pulley, a compressor including a driven pulley, a belt connecting said pulleys, means for controlling lthe output pressure of said compressor, and a movable member for simultaneously changing the tension on said belt, changing the pitch of and changing the operation of said output pressure control means.

10. In combination, a storage tank for compressed air or the like,.a platform mounted on said tank, a compressor secured -to said platform, a base movably mounted on said platform, a motor mounted on -said base, a relief valve mechanism ymounted on said tank, and resilient mean-s carried by sai-d base for controlling said relief valve in response rto movement of said base.

1l. In combination, a compressor, means for driving said compressor .at variable speed, valve means for regulating the pressure output of said compressor, :a movable member for varying said compressor speed, and a spring-urged element carried by said movable means for rendering a part of said valve means inoperative when said speed is changed.

l2. In a compressed air supply system having a s-torage tank, a compressor, and a drive motor, the combination which includes means for varying the drive between said motor and said comchange the speed and volumetric output of said compressor without material change in the speed of said motor, valve means for resaid tank at a low range when said Vcompressor rapidly, and means car-ried by said drive-varying means for rendering said valve means inoperative when Ithe speed of said compressor is reduced.

13. In a system'of the character described, the combination of a storage tank, a low pressure relief valve, a high pressurev safety valve, spring means for closing each of said valves, control means for varying the rate of sup-ply of a fluid to said storage tank, and means operable by said control lmeans to apply resilient force, in addition -to said spring means, to sai-d low pressure relief valve to hold `it closed at pressures substantially below the operating pressure of said safety valve.

BURR W. MANTLE.

REFERENCES' CITED The following references are of record in the file of this patent:

France 

